ViewInfo is becoming a smart class, not a dumb struct

Now it has:
A constructor
XML attribute serializer functions (but no XML tag of its own)

Also removed unused lastZoom

src/ViewInfo.cpp

@@ -0,0 +1,66 @@
+/**********************************************************************
+
+Audacity: A Digital Audio Editor
+
+ViewInfo.cpp
+
+Paul Licameli
+
+**********************************************************************/
+
+#include "ViewInfo.h"
+
+#include "Internat.h"
+#include "xml/XMLWriter.h"
+
+ViewInfo::ViewInfo(double start, double screenDuration, double pixelsPerSecond)
+   : selectedRegion()
+   , track(0)
+   , vpos(0)
+   , h(start)
+   , screen(screenDuration)
+   , total(screen)
+   , zoom(pixelsPerSecond)
+
+   , sbarH(0)
+   , sbarScreen(1)
+   , sbarTotal(1)
+   , sbarScale(1.0)
+   , scrollStep(16)
+
+   , bUpdateTrackIndicator(true)
+{
+}
+
+void ViewInfo::WriteXMLAttributes(XMLWriter &xmlFile)
+{
+   selectedRegion.WriteXMLAttributes(xmlFile, wxT("sel0"), wxT("sel1"));
+   xmlFile.WriteAttr(wxT("vpos"), vpos);
+   xmlFile.WriteAttr(wxT("h"), h, 10);
+   xmlFile.WriteAttr(wxT("zoom"), zoom, 10);
+}
+
+bool ViewInfo::ReadXMLAttribute(const wxChar *attr, const wxChar *value)
+{
+   if (selectedRegion.HandleXMLAttribute(attr, value, wxT("sel0"), wxT("sel1")))
+      return true;
+
+   if (!wxStrcmp(attr, wxT("vpos"))) {
+      long longVpos;
+      wxString(value).ToLong(&longVpos);
+      vpos = int(longVpos);
+      return true;
+   }
+
+   if (!wxStrcmp(attr, wxT("h"))) {
+      Internat::CompatibleToDouble(value, &h);
+      return true;
+   }
+
+   if (!wxStrcmp(attr, wxT("zoom"))) {
+      Internat::CompatibleToDouble(value, &zoom);
+      return true;
+   }
+
+   return false;
+}